There's frugal and there is foolish:

It's electrically a Bad Idea ... they are not intended to be lying on the gorund and can short out, resulting in blowing all kinds of circuits and maybe even starting fires.

Also, they have higher resistance than a genuine extension cord, and load down the circuits - also can lead to overheating and blowing fuses.

I'm all for reuse and recycling, but LazyGardens is making a valid point. Those light strings aren't made to carry alot of extra amperage. I never connect more than 2 strings of lights on our tree, for example.

At least leave in all the non-functioning light bulbs then. That way those sockets are protected from accidental contact with something. Like parts of an ornament. I believe, those sockets still have electricity flowing to them, just like an outlet in the wall.

A home fire is not worth the cost of an electrical cord. You have good intentions, reusing the cord. But about the only reuses I'd want to do are as maybe string to tie up tomato plants, or something else that doesn't involve electricity.

Did anyone actually read my original post? The three arborvitae are in fact outside and they have no ornaments. The lights strands aren't all connected to each other; there is a grounded, multiple-plug thingie. Each strand has only 50 lights. Everything is on a timer. The ONE nonfunctioning cord is a 25-light string. I was not recommending everyone abandon use of extension cords; it was just a quick fix solution kind of thing that worked for me in this instance. I have a ton of experience running and connecting Xmas lights. I also make candles and have made bonfires; which is to say, I respect fire and would not do something obviously dangerous.

I don't see the problem. People lay lights on their lawns down here all the time. I guess it's different, since our grass isn't dead and crispy, but as long as you replace it as soon as possible, I think it should be o.k.

My brother is an electrician, and he says the danger lies in the empty sockets getting dew in them and shorting out, not in the load on the string, because there actually is no load on it since it has no working lights. It's just a conduit.

umm Garden Faerie,

I'm sheepishly going to admit I noticed I have lights out there on my bushes with empty sockets. Shame on me. I'm going to have to find some burned out ones to fill the empty sockets, so I can follow my own darn advice!! Sorry to have sounded ornery in my earlier post. (I should have said branches instead of ornaments, you did mention the bushes.)